Overview of tumor-infiltrating lymphocyte (TIL) therapy. Tumors are surgically resected from patients, and tumor-infiltrating lymphocytes (TILs) are isolated and expanded ex vivo. These cells may either be infused without modification or genetically engineered. Engineered TILs include CAR (chimeric antigen receptor) TILs, checkpoint protein knockout (KO) TILs (e.g., programmed cell death protein 1 (PD-1) KO), and TILs expressing cytokine (e.g., interleukin-15 or IL-15) or chemokine receptor (e.g., CXC chemokine receptor 2 or CXCR2) to enhance persistence, function, or trafficking. Upon reinfusion into the patient, activated TILs specifically home to and target cancer cells, mediating effective tumor cell killing and potentially leading to durable cancer regression.